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I've noticed that when it's the equinox on this planet I'm making, the sun seems to cast a double shadow on the planet. How come the planet's ring seems to make two shadows with a space in between, instead of one "line" shadow. Is this accurate to real life, or a quirk of the rendering engine I'm using?
This might happen if you model the ring as opaque but of very little thickness and in the same plane as the vector between the planet and the sun Seen edge on from the equator, the ring would block none of the sun's light, but from a little north or south of the equator, the ring would block more of one hemisphere of the sun.
So I would check first if your geometry has things lined up too perfectly before considering a fault in the rendering engine.
The pattern is possible if there is a very large gap between two rings. Based on the spacing of the shadows, the gap would be at least as wide as a ring.
If there is only one ring, then it likely is a quirk of the engine.
The shadow cast by the rings onto Saturn is much more pronounced as shown by the Cassini spacecraft (e.g. here). Mind also, that the shadow is comparatively sharper than on Earth as the sun's apparent diameter is smaller at the ring planets' distance.
And, of course, the intensity of the shadow depends on the density of the rings - and the obliquity of the rings wrt light direction; they are extremely thin, and not very much packed with material, yet when you look through them nearly radially, they still block most if not all light.
It is very possible.
The intensity of the shadow depends on the density of the rings - and the obliquity of the rings wrt light direction; they are extremely thin, and not very much packed with material, yet when you look through them nearly.
Astronomical rings (Latin: annuli astronomici),  also known as Gemma's rings, are an early astronomical instrument. The instrument consists of three rings, representing the celestial equator, declination, and the meridian.
It can be used as a sun dial to tell time, if the approximate latitude and season is known, or to tell latitude, if the time is known or observed (at solar noon). It may be considered to be a simplified, portable armillary sphere, or a more complex form of astrolabe.
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House Focused Wheel Charts
Can a standard 2D wheel chart be better at taking into account planetary latitude? The answer is yes, if it is displayed in an alternative fashion.
Standard wheel charts are "sign focused", which means that a planet is plotted within the wheel based only on its sign position or zodiac longitude, and its latitude is ignored. Wheel charts can instead be "house focused", which means that the graphical position of where a planet is placed around the wheel will be its proportion through the 3D house. (In other words, the planet's proportion through the 3D house or percentage across the prime vertical on the local horizon, will be used to position the planet between the two appropriate house cusps on the wheel.) The result will cause planets to seem to move, or even seem to be in a different sign (however they will always be in the right house). That's the reverse of a standard "sign focused" wheel which will always position planets in the right sign (however they may be in the wrong 3D house). If one wants a graphical display accurate for both zodiac sign positions and 3D house positions at the same time, then they should use a chart sphere.
See below for an example of "sign focused" and "house focused" wheels displayed side by size. On the left is a standard "sign focused" wheel. The correct zodiac position of each planet is indicated by the planet's positioning within the surrounding ring of signs. Similarly, the standard house position of each planet is indicated by the planet's positioning within the surrounding ring of houses. However, since the wheel doesn't do anything with planetary latitude, the apparent house may not be the correct 3D house. On the right is a "house focused" wheel. The correct 3D house position of each planet is indicated by the planet's positioning within the surrounding ring of houses. However, the sign position of each planet isn't necessarily the positioning within the surrounding ring of signs. Notice how planets are positioned differently in the two wheels, usually subtly but sometimes significantly, especially for the fixed stars Sirius and Polaris.
Left: Standard "sign focused" wheel. Right: Alternative "house focused" wheel.
Note if the house system is Campanus, than switching between "sign focused" and "house focused" for a wheel chart will result in objects like the Sun and lunar Nodes not moving at all. That's because those objects are on the ecliptic (i.e. at 0 latitude) and Campanus houses and 3D houses have the same cusp points for objects on the ecliptic.
In Astrolog, if you turn on the "3D Houses" setting, then its standard wheel chart will be displayed "house focused" instead of "sign focused".
Solar System Observing Program - Outer Solar System
Jupiter: The Great Red Spot
Jupiter is by far the easiest planet to observe. Its giant disk offers the most detail to the amateur observer. Even at its smallest it is 30 arc-seconds in diameter, and at opposition it can be almost 50 arc-seconds, twice the size of Mars even though Jupiter is ten times further away from us! You are to time the rotation of the Red Spot across the center of the disk of the planet Jupiter. In the "Calendar Notes" column in Sky and Telescope magazine the dates and times are given when this famous feature on Jupiter is due to cross the Central Meridian of the planet. The Central Meridian (CM) is a line drawn from the planet's north pole to its south pole dividing the great globe into two equal eastern and western sections. This project will require three timings. The first is the time at which the leading edge of the spot crosses the CM. The second is the time at which the spot appears centered exactly on the CM. The third is the time at which the trailing edge of the spot reached the CM. Use the S&T column to guide your observing sessions. If you can only make one timing, make it number two, the central transit time. Access to a WWV time signal is preferable but if this is impossible, the observation is still acceptable. State if WWV or another standard time source was used in making your report. Do not forget to convert to Universal Time. During the past few years the Great Red Spot has been very pale and should perhaps be known as the Great Pale Salmon Colored Spot!
Jupiter: The Galilean Satellites (*B*)
Ever since Galileo it has been noted that the planet Jupiter and its four brightest and largest satellites form a kind of miniature solar system with a speeded up time scale. This magnification of time scale makes the system specially interesting to those who study potential changes in orbital mechanics. We have observing data on Jupiter's moons going back about 300 years. This consists of the recorded times when a satellite disappeared on entering Jupiter's shadow or reappeared upon exiting from it. Studying this data makes it possible to determine if Jupiter' satellite's orbits, and by inference, planetary orbits, change over periods of time. These eclipses are spectacular phenomena to watch in a small telescope. Since timings require a WWV time signal receiver. For this exercise we will only ask you to sketch the satellite positions on the this page for six consecutive nights identifying each satellite in your sketches. Include a copy of them in your report. As much as possible, try not to skip more that one night between consecutive viewings. The "Jupiter's Moons" chart in the Almanac section of astronomy magazines each month will help you to identify the individual moons.
To show the East-West direction of your sketches show with an arrow the direction of drift in your field-of-view without a drive running.
Jupiter: The Cloud Belts (*B*)
The first thing that comes to a person's attention when looking at the disk of the great planet Jupiter are the striated clouds of it's turbulent atmosphere. Fascinating and compelling, even a modest telescope reveals a good amount of detail, but always leaves you yearning for more. Through the years a system of nomenclature has been applied to the alternating dark and light areas called belts and zones, respectively. Coupled with the giants fast rate of spin (Jupiter's bulk rotates once in a little under ten hours) even the casual observer can notice something new. Below is a detailed list of the main cloud bands. Not all are always present all of the time. Jupiter's dynamics are too complicated for that. How many can you see? Make your own sketch and label those parts that seem to match up with the accompanying diagram. Include a copy of your sketch in your report.
Do not worry about a lot of detail. In fact Jupiter rotates so rapidly that features may move if you take too long to work on details. NOTE: Your telescope may show Jupiter inverted.
To show the East-West direction of your sketch show with an arrow the direction of drift in your field-of-view without a drive running.
Jupiter: Satellite Discovery (*B*)
On January 7, 1610 Galileo Galilei observed the planet Jupiter with his fourth and latest telescope. He had "spared no time and expense" in its production. With it he saw three small bright stars near the bright planet and assumed that they were fixed background stars. The next night he observed the Jovian planet again and was amazed to discover that the "stars" had changed their positions relative to the planet's disk. Very perplexing! Within a week he had seen all four of what we now call the Galileian satellites of Jupiter.
Galileo was using a primitive simple telescope magnifying about twenty times. Can you duplicate his feat with the modern lenses of a pair of binoculars?
It is important that the binoculars be held perfectly steady for the eye to pick out the tiny moons next to Jupiter's glare. Any movement, even the blood pumping through your veins will make them difficult to see. Try bracing your binoculars against a solid structure like a telephone pole or the roof of a car. Better yet, mount them on a tripod. Observe the satellites for several days and then describe your experience.
Jupiter: Satellite Shadow Transits
Shadow transits occur quite often and are a phenomenon that can easily be seen by the amateur. The shadows cast by the Galilean satellites are seen as tiny black dots slowly proceeding across the cloud tops of the giant planet.
Your task is to determine which of the four largest Jovian moons is casting the shadow. First you need to know if Jupiter is approaching its yearly opposition or if opposition has already passed. If Jupiter is moving toward its opposition then the shadow precedes the satellite. The moon's shadow will fall on the planet while the moon itself is still nearing the planet's limb. If opposition has passed, the moon will cross the planet's disc first, followed by its shadow. By consulting a Galilean Satellite Chart in an astronomy periodical you should be able to determine which satellite is casting the shadow. Which satellite was it?
Jupiter: Satellite Transits
Watching the Galilean Moons transit the disk of Jupiter is considerably more of a challenge than watching their corresponding shadows. The tiny little disks are similar in color to their parent planet so the satellite quickly gets lost from view in its frontal passage. The satellites can often be seen under the right conditions with larger apertures, for a few minutes, while still on the edge of Jupiter's limb. The limb tends to be slightly darker than the face of the planet itself. The contrast between the two helps the satellite to show up. The slow ingress or egress varies with each satellite. Io and Europa, being inner satellites, take only about two and a half minutes to ease onto or off of Jupiter's limb. Ganymede moves much more slowly, taking seven minutes, and Callisto crawls across the limb for nine minutes. If you are able to detect these ingresses or egresses, time them with a stop watch and compare the times with those just given. An alternative project would be to time the ingress or egress of one of the satellites into or out of Jupiter's shadow. What satellite did you time?
Jupiter: Satellite Eclipses (*B*)
Eclipses of the Galilean satellites occur as they move into or out of Jupiter’s shadow. This is different than an Occultation (see next requirement). Time the disappearance or reappearance of one of these satellites by using a radio tuned to the WWV National Time Standards signal out of Ft. Collins, Colorado. Then compare it to the time printed in the astronomy periodicals. Note the time when the satellite completely disappears into or reappears from behind Jupiter's shadow. Timing a reappearance is much more difficult since you do not know precisely when or where it will appear. Note the name of the moon that you observed.
Jupiter: Satellite Occultations (*B*)
Occultations of the Galilean satellites occur as they move behind or out from behind the planet Jupiter. This is different than an Eclipse (see previous requirement). Time the disappearance or reappearance of one of these satellites by using a radio tuned to the WWV National Time Standards signal out of Ft. Collins, Colorado. Then compare it to the time printed in the astronomy periodicals. Note the time when the satellite completely disappears or reappears from behind Jupiter. Timing a reappearance is much more difficult since you do not know precisely when or where it will appear. Note the name of the moon that you observed.
Saturn: The Rings (*B* They will appear as "ears" in binoculars)
Saturn is the most impressive object in the solar system and surely one of the most beautiful. Saturn is the only ringed planet whose rings are visible in the amateur's telescope. On a clear steady night, nothing rivals the sharp divisions and contrast seen in Saturn's ring system. Because of Saturn's considerable distance, high powers must be used. Under average conditions use a power of about 40X per inch of telescope aperture. However, do not sacrifice a clear image for the sake of a larger one. Make a sketch of what you see. Using a pre-drawn outline for your drawing can save a lot of time and effort at the eyepiece. The "Planetary Data" section of the astronomy magazines is an excellent resource for this. Place an arrow on your drawing to indicate the direction of drift when your scope is not tracking. Include a copy of your sketch in your report.
1. The day/month/year/time________________________________________
2. The seeing conditions___________________________________________
3. The aperture of the telescope._____________________________________
4. The focal length of the telescope.___________________________________
5. The focal length of your telescopes eyepiece.__________________________
6. Your own observational comments and impressions.____________________
Saturn: The Cassini Division
Within the three major rings that can be seen through the amateur telescope is the prominent gap known as the Cassini Division. It separates the "B" Ring, the brightest ring, from the "A" Ring and appears as a fine black line circling the planet. It is most easily seen on the two protrusions of the rings on either side of the planet known as ansae.
The axial tilt of Saturn and the inclination of Saturn's orbit compared with the Earth's, combine to cause the
plane of Saturn's rings to change their tilt. About every 7.25 years the rings go from edge-on to fully open. Your ability to see the Cassini Division will vary depending on how "open" or "edge-on" the rings are. Seeing and aperture size will also affect your ability.
Describe your view of the Cassini Division. Can you see it? Can you barely see it or does it "jump out at you?" How complete a circle of the rings can you detect?
Saturn: Disk Markings
At first glance the face of Saturn's disk seems rather boring, a bland creamy-yellow ball. Less than half the apparent diameter of Jupiter with proportionately duller markings, Saturn requires diligent study and a tranquil night of seeing. The greater your observing skill or equipment, the more subtle are the details you will see.
You should be able to tell that one hemisphere is decidedly darker than the other Can you tell which one? Be certain you know if your telescope shows an upright or an inverted image. Belts, zones and spots similar to Jupiter's can sometimes be glimpsed through the planet's top layer of obscuring haze. They are subtle. What do you see? Record your impressions.
Saturn: The Satellites (*B* if Titan is visible in binoculars)
Of all the satellites of Saturn, only six of them can be seen in telescopes with moderate sized apertures. How many can you spot?
|Magnitude||Orbital Period (Earth Days)||Recommended Aperture|
How many satellites you will be able to see will depend a great deal on atmospheric conditions . For example, I have seen all of them in a six-inch. In contrast with Jupiter, where all four moons orbital plane is nearly a straight line from Earth's viewpoint, Saturn's equatorial plane is considerably more tilted. This means that the orbits of the satellites can vary from a nearly straight line configuration to that of nearly a 30° ellipse depending on where Saturn and Earth are located in their orbits. This inclination changes at about a 15 year interval. Finder charts can be found in astronomy periodicals that will help you determine which of the Saturnian satellites you are seeing.
A note on Iapetus. The magnitude variation can be explained by the fact that it has two vastly different hemispheres. One reflects light almost two magnitudes brighter than the other. What satellites did you see?
Uranus Locating (*B*)
In 1781 the first non-classical planet was discovered by amateur astronomer William Herschel. The discovery changed Herschel's life forever and was a blow to astrologers who by their "craft" had no inkling that a seventh planet existed. Actually the planet had been seen and charted years before on no fewer than seventeen different occasions. Uranus is visible to the dark adapted naked eye under good skies. But the astronomers simply added it to their charts just like any other sixth magnitude star. It was Herschel who finally had enough resolving power and the observer's eye who could tell it had, in fact, a tiny disk, and was not a simple star-like point. He first suspected the tiny object to be a distant comet and took a series of measurements of its position. It was somewhat later that he realized its true nature.
It is much easier today for you and I. The 3.8 arc-second greenish disk shines at a magnitude of 5.7 and can be readily found using locator charts published in the astronomical periodicals. Give a verbal description your eyepiece impression.
Neptune Locating (*B*)
Although similar in size and appearance as Uranus, Neptune's distance averages over one billion miles further from the Earth. This great distance makes its apparent diameter about 2-1/2 arc-seconds, a little over half the size of Uranus.
The 7.6th magnitude bluish dot will probably look stellar, for its tiny disk is near the resolving limit of most amateur telescopes. Consult your favorite astronomy periodical to find out where it is currently located. Write a verbal description of your impression.
When the IAU made their decision to include a new class of objects in the Solar System called Dwarf Planets, Pluto was demoted from Planet to Dwarf Planet. Besides Ceres, it is the only Dwarf Planet that may be visible in a backyard telescope, but at magnitude 13.8 it may require a large telescope. The third Dwarf Planet, as of mid-2008 is Eris. It is located far beyond Pluto and far beyond the capabilities of backyard telescopes. Locate and observe Pluto, and sketch the starfield from your observation. Note the time and date of your observation.
Those projects identified with a (*B*) are the ones that can be used towards the Binocular Solar System Observing Certificate.
Is this render of a ringed planet's shadow accurate? - Astronomy
Creating planets of the solar system with Blender
These instructions will guide you through creating planets of the solar system in 3D using Blender and its Python API. At the end, you will have written a Python script which creates your planets, their orbits and even animates their rotation from scratch in one go. If you get stuck at some point, you can contact me at [email protected]
Following files are provided/needed:
- : a blender file with basic setup : a simple script for creating one planet : file with most basic parameters for each planet of the solar system and the sun : directory with texture maps of the planets, 17 MB : contains two functions for adding rings around Saturn and Uranus
- (Extra:) animate_camera.py: a script that sets the camera moving along a path looking at a certain object
- Blender (download from blender.org). These instructions were only tested with version 2.75. I expect them to work with versions from
It helps, if you are already a bit familiar with Blender's graphical user interface. Look at e.g. the Blender manual or follow these short Blender basics videos.
Open planets-template.blend with Blender from the command line:
Go to File -> Save As to save it under a custom name, e.g. just planets.blend .
Your 3D scene is shown in the 3D view area, that's the big central area. The template already contains a camera, a bright point lamp in the center to illuminate the planets you are going to create and a dark blue world background with a bit environment light switched on so that shadows are not too dark. You don't see its effects now, only later, when rendering your scene ( F12 ).
The window layout is already changed to Scripting for you (in the top menu bar, next to File , Render , Window and Help ). Go to the Text Editor area, (left main area) and load a script by selecting Text -> Open Text Block and choosing create_planet.py .
Select Text -> Run Script to execute the script. A blue sphere called Planet-Earth should appear in your 3D view.
If this works, then you can go ahead, expand the script and experiment with the following tasks. If it didn't work, check the output in the console from which you started Blender for error messages.
Look in the Python script in your Text area for the add_sphere -function. Improve it such that the size (radius) of the sphere is provided as an additional parameter. This should be used in Blender's primitive_uv_sphere_add function to create the sphere.
Provide e.g. size=2 in the main -function when creating the sphere and rerun your script. Check if the size has changed correctly. Note that the script contains a delete_objects -function that removes all objects with names matching Planet* from the scene. This is useful to cleanup before recreating your planet.
Adjust the material settings in the add_material function to create a planet with a different base color (e.g. red for diffuse_color ) and no specular. Colors are given as RGB-triplets in Blender, so red would be [1,0,0] .
So far, all these things can be done much faster via the interface. But such a script becomes very useful when creating more than one planet at once. Let's do this!
Write a read-routine to read planet and sun parameters from the provided csv-file. Blender comes with bundled Python that also includes the csv-module for reading comma-separated value files, which makes this task very easy, e.g like this:
Be careful to provide the correct (full) path to your csv-file. Alternatively you can also create a dictionary or array with parameters for different planets directly in your script. The parameters we use here are:
- name of the planet (or sun)
- radius of the planet (at equator), in km
- art_distance - artificial distance for good visual impression, in Blender units
- distance of the planet from the sun (semi-major axis)
- flattening of the planet
- tilt of the planet's axis
- rotperiod - time for rotation of the planet around its axis in days
- eccentricity of the planet's orbit
- orbitperiod - time for rotation of the planet on its orbit around the sun
- texture image for the planet
- color RGB triplet for the planet
In your main -function, write a loop to create more than one planet at once, with different names and sizes. Use the column art_distance from the provided csv-file to set the planets apart, e.g. along the + x -axis, using location when adding the sphere.
Take care to scale down the radii of the planets and the Sun to something between 0 and 10 Blender units, otherwise they may be too big to be visible in your Blender scene. (A basic size scale factor of 1/100,000 is a good value. For better visual impressions, increase the size of rocklike planets (Mercury, Venus, Earth, Mars) by a factor of 6, gas planets by a factor of 2.)
The Sun is special, since it is a self-glowing star. Thus its material needs to be adjusted. In general, you can always discover the available attributes for objects and materials via the Python Console:
First get the Sun-object: obj = bpy.data.objects['Planet-Sun'] .
Type obj. and press Ctrl + Space in the console to get autocomplete suggestions.
You can select the (first) material of your object using:
mat = obj.material_slots.material .
Type mat. and press Ctrl + Space in the console to explore the available attributes. You can also set them here and see their effects immediately.
These settings could also be adjusted in the GUI, in the Properties area, Material tab, in sections Shading and Shadow . They ensure that the Sun does not receive any shadows and does not cast any.
It's boring if all the planets have got the same color, so use a different color triplet for each planet. You can use the values from the file (parse them and convert them to a list of three values) or choose your own. Pass the color-triplet on to the add_material function, use it for diffuse_color in the script and rerun the script. Check, if every planet got its own color now.
Adjust the position of your camera, so you get a good view on all your planets. (Check by going into Camera View: View, Camera or Numpad 0 .) Render your scene with Render (top menu), Render Image or hit F12 .
Let's make the planets even prettier by adding an image texture map to each of them. Most planet textures are freely available from NASA. Download your own texture maps or use those from the textures-directory. Adjust the name of the texture image for each planet in your csv-file/dictionary.
Enable the add_texture function in the script's main -function. Make sure to provide the correct path to your images otherwise your script will fail. This function will load the image to a texture and map it using spherical coordinates.
Rerun your script. The texture will only be visible when rendered, so render your scene again ( F12 ).
- Actually, planets are rarely exact spheres, but mostly a bit flattened in z-direction. This is described by the flattening parameter, given e.g. at Wikipedia for each planet. 0 flattening is a perfect sphere. Adjust each planet-sphere's z -scale by the factor 1-flattening in your script.
Improve your script even further by adding a tilt to the planet's axis. The axial tilt is defined as deviation from the axis perpendicular to the planet's orbit, with Earth's north pole pointing upwards. The true direction to which the planet's north pole points is usually given in Earth's coordinate system. For simplicity, the provided csv-file already gives the correct precalculated rotation angles around x, y and z-axes for each planet in the global coordinate system. Thus you only need to set:
rotation_euler.x = tilt_x/180. * pi
etc. The angles in the file are given in degrees, thus they must be converted to radians first using angle[rad] = angle[degree] / 180 * pi.
If you do not want to set pi manually, import the math module to use math.pi instead.
Saturn is popular for its prominent ring system. Such rings are a bit tricky to set up, so there are functions prepared that take care of this for you, stored in rings.py . This uses more advances techniques which we won't discuss here. In principle, for Saturn we add a disk with a hole and put a ring texture on top of it for Uranus we create one circle with a thin thickness.
Copy the functions over or load them as a module by adding following lines at the beginning of your script:
The reload-line ensures that the rings-module is reloaded every time you run the script. This is important if you want to make custom changes there.
Add calls for the functions add_saturn_rings and add_uranus_rings to your main function. Neptune and Jupiter also have rings, but they are very thin and we'll skip them here.
Add a circle as orbit path for each planet (not for the Sun!), using art_distance for radius. This can be done via Blender's interface, Add , Curve , Circle .
Check in the log-output (Info window at the top) which function was used. Write your own add_orbit -function for your script to add an orbit circle for each planet. Do not make an orbit path for the Sun.
Name the orbit paths e.g. 'Planet-Earth-Orbit' etc. If you use the same 'Planet-' prefix as for the planet spheres, they will also be automatically deleted every time you run the script again.
Adjust the circles' resolution to increase the number of points for the curve and thus its smoothness (e.g. 60). You can find this setting in the Properties area at the right side, in the Data tab (small line symbol). Add this to your add_orbit function as well.
The circles cannot be seen in a rendered image, unless you give them some thickness. Thus increase the circles' thickness by setting the bevel depth to 0.006 or higher. In the interface, these setting are adjusted in the Properties area, at the tab for Data (bend curve symbol). Here you can look for the correct Blender attributes for your circle object and experiment which settings look good for you. Add them to your script as well.
You may want to add a material to your orbits and adjust its shadow and shading options, so that orbits do not cast or receive any shadows. This is achieved with exactly the same settings as for the Sun material which was explained above.
In fact, the planets move on ellipses, with the Sun at one of the focal points. We'll ignore this in this workshop and stick to the simplified circles.
Take the orbit eccentricity into account: shift the orbit path, so the sun lies at one of the focal points of the ellipse. I.e.: shift it in x-direction by a*ecc (semi-major axis times eccentricity). Scale the x-direction by a/distance, the y-direction by b/distance. b is the semi-minor axis, b = a*sqrt(1-ecc**2) . (Don't forget import math for sqrt!)
The orbit orientation is not yet correct - in truth, the orbit axes of the planets are not aligned! But taking the true orientation and also the inclination angle against e.g. Earth's orbit plane into account is beyond the scope of this workshop.
Camera Animation (may be skipped here)
Let's get the camera moving and add a camera path. Follow the next steps first via Blender's graphical interface, then check the log-output and the mouse-over tips for the functions and attributes to script this part as well.
- Add a circle via Add , Curve , Circle . Rename it to something like CameraPath. Set its location to (0,0,0) ( Alt + G ). Scale it such that there is still some distance between the circle and the sun (view it from top view to check this, Numpad 7 scale factor
Split the Python console window horizontally and switch the new frame to Timeline. Click and drag the green line to move forward/backward in time. Can you see the camera moving?
We are not yet done, the camera still looks away from the planets. We need to constrain its look-direction as well by adding an empty object to look at and another constraint:
- Add an empty using Add , Empty , Cube . This adds a cube-object that will not be rendered. Place it e.g. directly at Jupiter.
- Add another constraint to your camera, choose Track To . This must be added below the Follow Path constraint. Select the just created empty object as target .
When you move the time slider, you should now see the camera always looking to your empty object.
Do the same steps via scripting (also see animate_camera.py ), in order to be able to reproduce them, when needed.
The camera moves quite fast, you can slow it down by adjusting the animation manually:
- Select the camera path, in Properties area switch to the Curve data tab and look for the Evaluation time . It is marked in green, because it is animated. Right click with the mouse and select Clear keyframes .
- In the timeline, choose frame 1. Set the curve's evaluation time to 0 and hit the I key while hovering over the evaluation time field. This sets a new animation keyframe (yellow).
- Now set the time to e.g. 500 frames, set the evaluation time of the curve to 100 and again hit I . This sets the second (final) keyframe. Your camera will now move along the whole path within 500 frames.
Further details of animations can be adjusted in the Graph Editor, we'll look into this in the next sections.
We will now let the planets move along their orbit paths.
First do it for one planet and its path in the interface, then code the steps by checking which functions were used in the log/hover info.
Reset the position of the planet to (0,0,0).
Select the planet's orbit. In the Properties area, switch to the Constraints tab. Click Add Object Constraint and select Follow Path .
As target , choose the planet's orbit path. This will constrain the movement of the planet to its path! It is important that the path's rotation angles are set to 0 here, otherwise the planet will "inherit" the rotation and appear upside down or otherwise rotated.
Split the Python Console window horizontally (drag the triangle) and switch the new window to Timeline (if you haven't done so yet). Here you can set start and end frame of your animation and set the current frame.
In order to get the planet moving, we need to set animation keyframes on the Evaluation time of the path:
- Select the orbit path. In Properties area switch to Curve data tab and look for the Evaluation time . If the field is green, then right click with the mouse and select Clear keyframes first to reset everything.
- In the timeline, choose frame 1. Set the curve's evaluation time to 0 and hit the I key while hovering over the evaluation time field. This sets a new animation keyframe (yellow).
- Now set the time in your timeline to some duration, e.g. 365 frames.
- Set the evaluation time of the curve to 100 and again hit the I key. This sets the second (final) keyframe.
- Click and drag the green line to move forward/backward in time between these two keyframes. Can you see the planets moving on their orbits now?
Switch the Python Console window to Graph Editor to fine tune your animation curve. When you have the orbit path selected, you should see a curve that represents the interpolation of the evaluation time between your two set keyframes. You can use the mouse wheel to zoom in and out and Shift + middle mouse button ( MMB ) to pan the area.
Adjust the interpolation type of the curve in the right toolbar within the Graph Editor (enable with T key, if you cannot see it). At Active keyframe, choose Interpolation : Linear instead of the default Bezier curve.
Planets also do not rotate only once, but repeatedly. To achieve this, we could repeat setting keyframes at multiples of the orbitperiod and evalution time, but we can simplify it by using a graph modifier. At Modifiers in the toolbar select Cycles and select Repeat with Offset for Before and After.
That's (nearly) it! Your planet should move now continuously around the Sun on its orbit.
There is still something not quite right: the planets of our solar system rotate counter-clockwise when seen from the northern side of the ecliptic, i.e. when seen from +z downwards in our Blender setup. But your planet currently moves in clock-wise direction! That's because your orbit circle has clock-wise direction. The easiest way to switch the orbit direction is to rotate it via the y -axis by 180 degrees. Add another rotation via its z -axis by 90 degrees to put the first point of the orbit along the +x-axis. Now Apply the orbit rotation: Object , Apply , Rotation . This applies the rotation to the points of the curve, they are all shifted now, and resets the rotation angles to 0. As mentioned already above, this is important for maintaining the correct planet orientation, otherwise the planet would inherit its orbits orientations.
Include all these steps in your script for each planet. Set the keyframes according to the actual orbit rotation period given in the planets-file ( orbitperiod ). This value is given in days use a timefactor to make your planets move slower or faster than 1 frame for 1 day.
Hint: use the keyframe_insert -function, e.g. like this: orbit.data.keyframe_insert(data_path="eval_time", frame=1)
If you used ellipses, then the speed of the planets should be faster closer to the sun (according to Kepler's laws). Blender does not easily allow to do that, so we will ignore this here. Just be aware that the true speed would be different than what we currently have.
Planets also rotate around their own axes, that's given by rotperiod in the file. This gets slightly more complicated than just adding animation keyframes for the z -rotation values, because the planet's axes are already tilted. If a z-rotation is added, then the planet would rotate around the current z-axis, not around the planet-axis. You can see this easily with Saturn and its rings or Earth, when changing the z-rotation value in the 3D view, properties panel (enable with N if it is hidden).
We therefore use a special trick: we add an axes object for each planet and assign it the axial tilt. Then we clear the rotation of the planet and parent it to the axes object. This has the effect that the planet is basically unrotated, but inherits the tilt from its parent axes object. Now it's possible to keyframe the z-rotation of the planet!
Use Add , Empty , Arrows in the interface and check from the log-output which function was used. Add this function in your script to create such arrows for each planet. Give it a name like Planet-Earth-Axes etc. for clear identification and to include it in the deleting process at the beginning of the script.
Assign the planet's tilt angles to the corresponding axes object.
Clear the planet's rotation angles, i.e. set them to (0,0,0).
Add the axes-object as parent to each planet. In the interface, select a planet, go to the Properties area, switch to the Object tab and look for Parent at the Relations-section. Here one can enter the axes object. Check the tooltip for the field to get an idea how to include setting the parent in your script.
So far, nothing much has changed, the planets should still look the same. But now we are ready to add the rotation animation. Let's do it first in the interface:
- Select a planet (not it's axes!).
- In the Timeline, set the time to frame 1.
- In 3D view, go to the properties region at the right side and look for the rotation. The z rotation should be 0. Hover with the mouse over this field and press the I key to insert a keyframe.
- Set the time to the rotation period, e.g. 10, set the rotation to 360 degrees and again insert a keyframe.
- Move the time slider to see the planet rotating around its axis.
- Switch your Python Console area (or any other) to the Graph Editor area, again set the Interpolation type to Linear .
- Add a Cycles modifier and set Before and After values to Repeat with Offset , just the same way as for the orbit animation. This ensures a continuous and smooth planet rotation.
Include these steps in your script, for each planet and for the Sun.
Render your animation by selecting Render , Render Animation in the top menu. The render resolution and other properties can be adjusted in the Properties area, at the Render tab (photo camera symbol). By default, Blender will create one png-image for each frame in the tmp -directory.
You can stop the rendering any time using the Esc key.
Play your rendered animation with Blender, using Render , Play Rendered Animation .
It is also possible to render your frames in the background, using the command line:
This will render the frames 1 to 600.
The solar system that we built up to now is still lacking in many details. Here are some suggestions to improve it further:
- Use real distances (scaled down by the same factor) for planets from the Sun.
- Switch on shadows for the lamp, so that rings and moons can cast shadows on their planets. This was switched off initially, because we had the planets unrealistically close to each other.
- Make orbits eccentric, use correct orbit orientation.
- Use true (non-uniform) speed along eccentric orbits.
- Use different image textures (e.g including clouds for Earth and Venus).
- Use animated textures, e.g. for the Sun to mimick evolving Sun spots, or for Earth to have different clouds evolving with time.
- Use UV-unwrapping for a more accurate mapping of textures to the sphere, especially at the poles.
- Add moons, minor planets and asteroids.
- Add stars in the background as reference system, maybe even the true stars from the sky, using a sky map.
If you made it this far: thanks for staying with me and congratulations! I hope you enjoyed this tutorial. For comments and suggestions, mistakes or questions, please send a mail to [email protected]
Interested in my final version of the Python script, which includes the steps explained in this tutorial? I've uploaded it here: create_planet_final.py. It doesn't contain the 'Further improvements' steps, however, since so far I didn't have enough time to include them all. If you manage to finish these, I would appreciate it if you share your final version! :-)
Saturn Shows New Ring
Saturnshowed off a newring in a snapshot just taken by NASA's Cassini spacecraft.
Thespacecraft, which entered the orbit of Saturnin July 2004, also revealed other dazzling features of the ringed planet,including wispyfingers of icy material stretching out tens of thousands of miles from themoon Enceladus.
Cassini's cameras took advantage of a 12-hour backlight provided by the Sun,which was directly behind Saturn. So as Cassini lurked in the shadow of Saturn,the planet's rings were brilliantly backlit by the passing Sun. Called a solaroccultation, this Sun-Saturn alignment typically lasts only about an hour, butthis time it was a half-day marathon.
The lengthyillumination of Saturn allowed Cassinito map the presence of microscopic particles that are not normally visibleacross the ring system. This level of detail gave astronomers the sharpest viewyet of Saturn's inner system, including the new ring.
Saturn'sring system is divided into seven main divisions, each designated by aletter of the alphabet. From the innermost to outermost ring, the divisionsare: D, C, B, A, F, G and E.
The newring is a tenuous feature and lies outside the brighter main rings of Saturn,but inside the G and E rings.
The ringcoincides with the orbits of Saturn's moons Janus and Epimetheus. Scientistsexpected meteoroid impacts on the two moons could kick off moon particles andinject them into Saturn's orbit. But they were surprised to find such adistinct ring structure in that region.
The 12-hourbacklight session enabled astronomers to see the entire E ring in one view, afeat that previously required several images of small sections of the ring.
Thesnapshot showed Enceladussweeping through the E ring, extending wispy, fingerlike projections into thering. The scientists suspect the 'fingers' consist of tiny ice particles beingejected from Enceladus'south polar geysers and into the E ring.
Is this render of a ringed planet's shadow accurate? - Astronomy
Pluto, originally the 9th planet was discovered in 1930. Since then, astronomers have searched for a 10th planet beyond the orbit of Pluto. Until recently, all that's resulted from this are number of unconfirmed reports and a few crackpot theories.
A number of trans-Neptunian objects (TNOs) -- objects farther away from the Sun than Neptune -- were discovered since 2000, but all were much smaller than Pluto and its moon Charon.
In 2002, Quaoar, a trans-Neptunian object with an estimated size larger than Charon was discovered by Chad Trujillo and Michael Brown, astronomers at Caltech. A year later, another TNO, Sedna, was shown to be nearly two-thirds Pluto's size.
In 2003, Trujillo and Brown discovered yet another TNO. This one has now (2006) been officially names Eris (after the goddess of discord (previously labeled 2003UB313 and nicknamed "Xena" by its discoverers). It has an estimated diameter at 2700 km, larger than Pluto's 2320 km diameter. It also has a moon, Dysnomia (in mythology the child of Eris) and nicknamed "Gabrielle", discovered in 2005.
In August 2006 Astronomers at the IAU debated the formal definition of a planet and created a new class, called dwarf planets of which Eris, Pluto and Ceres (the largest of the asteroid belt members) are the first members. They do not (under the new definition) get to be "classic" planets, as they are not large enough to dominate their orbits. Sedna and Quaoarare also members of this class, pending a formal confirmation of their shape. Another TNO, Makemake, which is three quarters the size of Pluto, was made a dwarf planet in 2008.
An artist's rendering of Eris (Xena), with the Sun in the background. Credit: Robert Hurt (IPAC)
In 2015, Caltech astronomers Konstantin Batygin and Mike Brown found theoritical evidence (not observational) of a giant planet about 20 times farther from the Sun than Npetune on average. The prediction of the so called Planet 9 is mathematical and could explain the unique orbits of at least five smaller objects in the outer Kuiper belt. As of January 2019, no observation of Planet Nine has been announced.
Artist's concept of a hypothetical planet orbiting far from the Sun. Credit: Caltech/R. Hurt (IPAC)
This page updated on January 28, 2019.
About the Author
Rebecca is a eighth-year graduate student in astronomy, with an interest in Saturn's rings.
Hubble Reveals The Beauty And Mystery Of Saturn’s Rings
Saturn and its spectacular rings, as imaged by the Hubble Space Telescope on July 4, 2020. Hubble . [+] takes an annual image of Saturn as part of the Outer Planets Atmospheres Legacy (OPAL) project.
NASA, ESA, A. Simon (Goddard Space Flight Center), M.H. Wong (University of California, Berkeley), and the OPAL Team
Right now, in Earth’s skies, Saturn appears at its biggest and brightest.
A view of tonight's midnight sky from 45 N latitude, which shows the relative positions of bright . [+] Saturn and even brighter Jupiter in the southern part of the sky. They rise in the southeast just as the Sun sets, then migrate towards the west over the course of the night. They are joined by a variety of meteor showers, including the Delta Aquariids.
Just look to the southeastern skies (from the northern hemisphere), slightly east of bright Jupiter.
Every year, there's one moment where Earth passes directly between the Sun and Saturn, occurring . [+] recently in the 2nd half of July. As captured by amateur astronomer Christian Gloor in 2019, this shows a view very close to what skywatchers will see through a telescope tonight, although the rings are slightly more edge-on this year than last year.
With Earth between the Sun and Saturn, it’s poised for spectacular viewing.
The seven extraterrestrial planets of the solar system: Mercury, Venus, Mars, Jupiter, Saturn, . [+] Uranus, Neptune. Photographed in 2019 with a Maksutov telescope from Mannheim and Stockach in Germany. The angular sizes and colors shown are accurate, but the brightnesses are not: Venus is some 63,000 times brighter than Neptune, or 12 astronomical magnitudes the same difference as between the full Moon and a typical bright star like Vega or Capella. Saturn's rings are incredibly prominent, and the only ringed system visible through a typical telescope.
But the true star of Saturn is its main rings, now tilted for excellent views.
A computer simulated view of what Saturn looks like from Earth during opposition in every year from . [+] 2001 through 2029. Note the 15 year repeating pattern of where the rings are maximally tilted or edge-on to the Earth. Right now, in 2020, the rings are becoming closer to edge-on, which they will achieve in 2024.
Every 15 years, the rings cycle from edge-on to maximum tilt and back again.
Details of Saturn's main, icy rings are visible in this sweeping view from Cassini of the planet's . [+] glorious ring system. The total span, from the innermost A ring to the outer F ring shown here, covers approximately 40,800 miles (65,700 km) and was photographed on November 26, 2008. The outermost rings, including the ring created by Enceladus and the Phoebe ring beyond that, are not shown.
NASA/JPL/Space Science Institute
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Although they reach over 70,000 kilometers in extent, they’re only 30 kilometers thick.
This 1990s-era image from NASA's Hubble Space Telescope shows Saturn in an unusual configuration: . [+] with its rings edge-on to us from our perspective. This occurs roughly every 15 years on a repeating basis, with the rings tilted at an angle the rest of the time. Saturn's giant moon Titan can be seen at left (with its shadow falling on the planet), while smaller moons appear to the right.
Erich Karkoschka (University of Arizona Lunar & Planetary Lab) and NASA/ESA
As a result, they briefly seemed to disappear in 1994, 2009, and will again in 2024.
From the vicinity of Saturn itself, NASA's Cassini mission was able to capture the shadows cast by . [+] various ice crystals from within the rings, showing the incredible relief of the thin rings and their shadows against the main rings themselves. Saturn's rings might extend for tens of thousands of kilometers in the radial dimension, but are only 30 km thick.
NASA/JPL/Space Science Institute
NASA’s Cassini mission previously captured long shadows cast by nearly edge-on sunlight.
This 2018 image from NASA's Hubble Space Telescope shows Saturn at opposition, with four of its . [+] moons visible and its rings shining brightly at nearly their maximum tilt with respect to our perspective. The banded structure of Saturn itself can also be seen, as can many of the gaps/divisions in the main ring system.
NASA, ESA, A. Simon (GSFC) and the OPAL Team, and J. DePasquale (STScI)
With no current Saturn orbiters, NASA’s Hubble provides our best views from afar.
Taken by the Cassini spacecraft with the Sun hidden behind Saturn, this backlit view of our Solar . [+] System's great ringed world contains a bonus: a few pixels that reveal the Earth-Moon system. This is one of the most distant photographs of Earth ever taken, but it still reveals our world as larger than a single pixel. The rings themselves appear glorious, and are composed of 99.9% water ice.
NASA / JPL / Space Science Institute / Cassini, boxes by E. Siegel
The rings are 99.9% water ice, and are comparable in total mass to Saturn’s 7th largest moon: Mimas.
Saturn's 7th largest moon, Mimas, appears to hover above the colorful rings. This image was taken by . [+] the Cassini spacecraft and, despite their enormous size differences, show two entities of comparable mass. Mimas is approximately twice the mass of the entirety of the ring system, despite the much larger apparent extent of the rings.
Universal Images Group via Getty Images
Saturn’s rings are quickly evaporating they’ll be gone in merely 300 million years.
This image of Saturn's rings, with the planet itself behind them, was taken by Cassini at a distance . [+] of 725,000 km from the planet. Due to the fact that the ring system is "raining" down material onto Saturn, we can conclude that the rings will be entirely gone, based on the current rate of mass loss, in another 300 million years.
NASA/JPL-Caltech/Space Science Institute
The evidence possibly points to their origin arising from a recently destroyed moon.
Within Saturn's rings, many small moons and moonlets, such as Daphnis, can be found. These objects . [+] are likely created by accreting particles, then destroyed by collisions and tidal forces. their uniform composition and decaying nature suggests that they were created relatively recently, with one longstanding theory contending that a larger, destroyed moon gave them their origin as little as tens but as many as hundreds of millions of years ago.
NASA / JPL-Caltech / Space Science Institute
Back when trilobites dominated the Earth, Saturn may not have had any rings at all.
The entirety of Saturn's main rings, from the inner D ring to the outer F ring, may be much newer . [+] than the rest of the Solar System. It's plausible that a few hundred million years ago, before the rise of the dinosaurs, these rings may not have existed at all. In another 300 million years ago, they likely will have disappeared entirely.
Until another Saturn-bound mission launches, telescopes like Hubble will provide our sharpest views.
While the age of Saturn's rings remains controversial, annual portraits from Hubble, such as this . [+] 2019 image, continue to shed insights on this fascinating giant planet. The changing north pole, in particular, can be seen by comparing the 2018, 2019, and 2020 images illustrated in this article.
NASA, ESA, A. Simon (GSFC), M.H. Wong (University of California, Berkeley), and the OPAL Team
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less smile more.
Barely bisected rings
Saturn’s shadow stretched beyond the edge of its rings for many years after the NASA/ESA/ASI Cassini spacecraft first arrived at Saturn, casting an ever-lengthening shadow that reached its maximum extent at the planet’s 2009 equinox. This image captured the moment in 2015 when the shrinking shadow just barely reached across the entire main ring system. The shadow will continue to shrink until the planet’s northern summer solstice, at which point it will once again start lengthening across the rings, reaching across them in 2019.
Like Earth, Saturn is tilted on its axis. And, just as on Earth, as the sun climbs higher in the sky, shadows get shorter. The projection of the planet’s shadow onto the rings shrinks and grows over the course of its 29-year-long orbit, as the angle of the Sun changes with respect to Saturn’s equator.
This view looks toward the sunlit side of the rings from about 11 degrees above the ring plane. The image was taken in visible light with the Cassini spacecraft wide-angle camera on 16 January 2015.
The view was obtained at a distance of approximately 1.6 million miles (2.5 million kilometres) from Saturn. Image scale is about 90 miles (150 kilometres) per pixel.
Saturn: Exploring the Ringed Planet
Find out more about Saturn and its moons in this 196-page special edition from Astronomy Now. [geot exclude_region=”US” ]Order from our online store.[/geot][geot region=”US” ]Order from our online store.[/geot]